It is known that after a print job, image densities of toner particles for colors printable by color printers or copiers are analyzed and adjusted to maintain the image densities at a desired density value. A common technique for monitoring quality of images printed by the color engines of the printers or copiers creates one or more test patches of toner particles for each color to measure a density of toner within each test patch for each of color. The test patches are imaged with the toner particles of a single color to a predetermined density. The predetermined density corresponds to the desired density which ensures that the color engine is maintaining the quality of images printed by a color engine at a visually acceptable level.
These known methods control densities of toner particles for one or more colors and single separations of color in color engines for printers or copiers to stabilize the overlay colors. The methods stabilize and control the overlay colors by independently controlling each of the single separations of color by maintaining the actual density value for each separation of color within the tolerance range associated with color. However, because of system variations in different color engines, the methods have difficulty controlling the four single separations of color to minimize an overall variation in the overlay colors. The methods independently control each of the single separations within a tolerance range to ensure that the color variation or a relative error for each single separation of color is maintained or is stabilized within a tolerance range.
However, large errors in the overlay colors occur when the actual density value of one or more of the single separations is offset upwardly with respect to the target value or has a positive value and one or more of the single separations is offset downwardly with respect to the target value or has a negative value. By having single separations of color within the tolerance ranges above the target value and below the target value, significant errors in the overlay colors are generated that are noticeable and visible to the eye of a user. Even though the actual density value for each of the single separations is located within the tolerance range, errors in the overlay colors may still be generated or created by the traditional methods for controlling the color separations or the densities of toner particles of more than one color. The errors in the overlay colors that are generated by the methods may thus be unacceptable even though the actual density value for each single separation is well within the tolerance range of the predetermined target value for each color.
A need, therefore, exists for a system and a method for controlling consistent color quality of overlay colors and single separations of color for a color engine of a printer or a copier. Moreover, a need exists for a system and a method for controlling consistent color quality which may minimize variation in overlay colors and maintain an actual density value for each single separation of color within a tolerance range of each color's target.